1. Field of the Invention
This invention relates to an energy recovering apparatus and method for a plasma display panel, and more particularly to an energy recovering apparatus and method for a plasma display panel wherein a charge time of the plasma display panel can be shortened with the aid of a compulsory resonance to thereby improve a discharge characteristic.
2. Description of the Related Art
Recently, there has been developed various flat panel devices that are capable of reducing a heavy weight and a large bulk, which are drawbacks of the cathode ray tube (CRT). Such flat panel display devices include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP) and an electro-luminescence display (ELD), etc.
The PDP of these flat panel display devices is a display device using a gas discharge, and has an advantage in that it is easy to manufacture a large-dimension panel. The PDP typically includes a three-electrode, alternating current (AC) surface discharge PDP that has three electrodes and is driven with an AC voltage as shown in FIG. 1.
Referring to FIG. 1, a discharge cell of the conventional three-electrode, AC surface-discharge PDP includes a first electrode 12Y and a second electrode 12Z provided on an upper substrate 10, and an address electrode 20X provided on a lower substrate 18.
On the upper substrate 10 provided with the first electrode 12Y and the second electrode 12Z in parallel, an upper dielectric layer 14 and a protective film 16 are disposed. Wall charges generated upon plasma discharge are accumulated into the upper dielectric layer 14. The protective film 16 prevents a damage of the upper dielectric layer 14 caused by a sputtering during the plasma discharge and improves the emission efficiency of secondary electrons. This protective film 16 is usually made from magnesium oxide (MgO).
A lower dielectric layer 22 and barrier ribs 24 are formed on the lower substrate 18 provided with the address electrode 20X. The surfaces of the lower dielectric layer 22 and the barrier ribs 24 are coated with a fluorescent material 26. The address electrode 20X is formed in a direction crossing the first electrode 12Y and the second electrode 12Z. The barrier rib 24 is formed in parallel to the address electrode 20X to prevent an ultraviolet ray and a visible light generated by a discharge from being leaked to the adjacent discharge cells. The phosphorous material 26 is excited by an ultraviolet ray generated during the plasma discharge to generate any one of red, green and blue visible light rays. An inactive gas for a gas discharge is injected into a discharge space defined between the upper and lower substrate 10 and 18 and the barrier rib 24.
Such a three-electrode, AC surface discharge PDP is driven with being separated into a number of sub-fields. In each sub-field interval, a light emission having a frequency proportional to a weighting value of a video data is conducted to provide a gray scale display. The sub-field is again divided into an initialization period, an address period, a sustain period and an erasure period.
Herein, the initialization period is a period for forming uniform wall charges on the discharge cell. The address period is a period for generating a selective address discharge in accordance with a logical value of the video data. The sustain period is a period for allowing a discharge cell in which the address discharge has been generated to sustain a discharge. The erasure period is a period for erasing a sustain discharge generated in the sustain period.
The address discharge and the sustain discharge of the AC surface-discharge PDP driven in the above manner requires a high voltage more than hundreds of volts. Accordingly, an energy recovering apparatus is used for the purpose of minimizing a driving power required for the address discharge and the sustain discharge. The energy recovering apparatus recovers a voltage between the first electrode 12Y and the second electrode 12Z, to thereby use the recovered voltage as a driving voltage upon the next discharge.
Referring to FIG. 2, energy recovering apparatus 30 and 32 of the PDP having been suggested by U.S. Pat. No. 5,081,400 of Weber are symmetrically arranged with respect to each other with having a panel capacitor Cp therebetween. The panel capacitor Cp is an equivalent expression of a capacitance formed between the first electrode Y and the second electrode Y. The first energy recovering apparatus 30 applies a sustain pulse to the first electrode Y. The second energy recovering apparatus 32 operates alternately with respect to the first energy recovering apparatus 30 to thereby apply a sustain pulse to the second electrode Z.
Hereinafter, configurations of conventional energy recovering apparatus of the PDP will be described with reference to the first energy recovering apparatus 30.
The first energy recovering apparatus 30 includes an inductor L connected between a panel capacitor Cp and a source capacitor Cs, first and third switches S1 and S3 connected, in parallel, between the source capacitor Cs and the inductor L, and second and fourth switches S2 and S4 connected, in parallel, between the panel capacitor Cp and the inductor L.
The second switch S2 is connected to a sustain voltage source VS while the fourth switch S4 is connected to a ground voltage source GND. The first to fourth switches S1 to S4 control a current flow.
The source capacitor Cs recovers and charges a voltage charged in the panel capacitor Cp upon sustain discharge and re-supply the charged voltage to the panel capacitor Cp. The source capacitor Cs is charged with a voltage Vs/2 equal to a half value of the sustain voltage source Vs.
The inductor L forms a natural resonance circuit along with the panel capacitor Cp. At this time, the conventional energy recovering apparatus allows a step of storing energy into the inductor L to overlap with a step of supplying the panel capacitor Cp with the energy stored in the inductor L.
Meanwhile, fifth and sixth diodes D5 and D6 provided between the first and second switches S1 and S2 and the inductor L, respectively prevent a current from flowing in a backward direction.
FIG. 3 is a timing diagram and a waveform diagram representing an on/off timing of switches in the first energy recovering apparatus and an output waveform of the panel capacitor.
An operation procedure of the energy recovering apparatus will be described assuming that 0 volt has been charged in the panel capacitor Cp and a Vs/2 voltage has been charged in the source capacitor Cs prior to a T1 interval.
In a T1 interval, the first switch S1 is turned on, to thereby form a current path extending from the source capacitor Cs, via the first switch S1, the inductor L, into the panel capacitor Cp. If the current path is formed, then a Vs/2voltage charged in the source capacitor Cs is applied to the panel capacitor Cp. At this time, a Vs voltage equal to twice the voltage of the source capacitor Cs is charged in the panel capacitor Cp because the inductor L and the panel capacitor Cs form a serial resonance circuit.
In a T2 interval, the second switch S2 is turned on. If the second switch S2 is turned on, then a voltage of the sustain voltage source Vs is applied to the first electrode Y. The voltage of the sustain voltage source Vs applied to the first electrode Y prevents a voltage Vcp of the panel capacitor Cp from falling into less than the sustain voltage source Vs to thereby cause a normal sustain discharge. Meanwhile, since the voltage Vcp of the panel capacitor Cp has risen into Vs in the T1 interval, a driving power supplied from the exterior for the purposing of causing the sustain discharge is minimized.
In a T3 interval, the first switch S1 is turned off. At this time, the first electrode Y sustains a voltage of the sustain voltage source Vs during the T3 interval. In a T4 interval, the second switch S2 is turned off while the third switch S3 is turned off. If the third switch S3 is turned off, then a current path extending from the panel capacitor Cp, via the inductor L and the third switch S3, into the source capacitor Cs is formed to recover a voltage Vcp charged in the panel capacitor Cp into the source capacitor Cs. At this time, a Vs/2voltage is charged in the source capacitor Cs.
In a T5 interval, the third switch S3 is turned while the fourth switch S4 is turned on. If the fourth switch S4 is turned on, then a current path between the panel capacitor Cp and the ground voltage source GND is formed, thereby allowing the voltage Vcp of the panel capacitor Cp to 0 volt. In a T6 interval, the T5 state is maintained during a certain time. In real, an alternating current driving pulse supplied to the first electrode Y and the second electrode Z allows the T1 to T6 intervals to be obtained with repeating periodically.
In the mean time, the second energy recovering apparatus 32 operates alternately with respect to the first energy recovering apparatus 30. Accordingly, a sustain pulse voltage Vs having a mutually contrary polarity is applied to the panel capacitor Cp. The sustain pulse voltage Vs having a mutually contrary polarity is applied to the panel capacitor Cp is applied, so that a sustain discharge can be generated from the discharge cells.
However, such conventional energy recovering apparatus 30 and 32 have a problem in that the first energy recovering apparatus 30 provided at the first electrode (Y) side and the second energy recovering apparatus 32 provided at the second electrode (Z) side operate individually to require many circuit elements such as a switching device, etc., and thus to raise a manufacturing cost. Furthermore, a lot of power consumption is caused by a conduction loss of a plurality of switches, such as a diode, a switch device and an inductor, etc., on the current path.